Surgeons frequently use a variety of different power tools during operative procedures. As with any surgical instruments, these tools must be sterilized prior to use. Generally these have been pneumatically powered or powered by AC current. This is problematic in that the air hose or power cord can interfere with operative procedures.
Over recent years more and more battery powered equipment has been developed. Battery cells, particularly lithium ion cells, and nickel cadmium cells provide sufficient power and are easily charged permitting them to be used with most electrical equipment. To be used with surgical equipment, the battery must be autoclavable. Typically lithium ion cells will vent out and be destroyed at about 80xc2x0 C. For maximum life, it is desirable to keep the temperature of lithium or Ni/Cd cells to less than 60xc2x0 C. Sterilization requires autoclaving typically at 136xc2x0 C. for four minutes to meet U.S. regulations or ten minutes to meet European regulations. Thus, this has limited the use of batteries for surgical instruments.
Another major concern is safety. Since autoclaves can run for 40 minutes, it is imperative that the cells not rupture or explode if they are inadvertently autoclaved for 40 minutes.
The present invention is premised on the realization that an autoclavable battery pack can be formed by providing a sealed battery case incorporating a plurality of cells. Separating the cells from the battery case is an insulating material that provides effective insulation to prevent the cells from reaching 80xc2x0 C. (preferably less than 60xc2x0 C.) during autoclave conditions. Typically the insulation should be one which has a thermal conductivity of 0.02 kilocalories per hour at 136xc2x0 C. or less. In a preferred embodiment, the insulation is expanded silica thermal insulation such as Microtherm HF(trademark) quilted insulator. In an optimum situation, sufficient insulation is employed to prevent the cell temperature from reaching 80xc2x0 C. when autoclaved for forty minutes at 136xc2x0 C.
The objects and advantages of the present invention will be further appreciated in light of the followed detailed description and drawings in which: